Pulmonary hypertension is a significant clinical entity severely affecting the longevity and quality of life for patients with either primary or secondary' forms of this disorder. Regardless of its underlying cause, pulmonary hypertension remains intractable to traditional pharmacotherapy. Recent basic genetic and preclinical pharmacological] studies suggest that newly developed agents modifying endothelin activity may have a potential role in pulmonary hypertension. Nonetheless, it is highly likely that general principles of pharmacology predictive of issues of non-specificity and adverse effects as well as target alterations leading to tachyphylaxis and desensitization will ultimately limit the use of new generation endothelin modifiers. In the current proposal, we suggest that advances in non-viral based genetic therapy may provide novel alternatives to traditional pharmacotherapy. In particular, delivery of antisense Oligodeoxynucleotides (ODN) to endothelin-1 lET-l) by immunoliposome can be used to down regulate pulmonary' endothelial ET-1 biosynthesis and similar application with RNA/DNA chimeric oligonucleotide may more permanently silence such expression. Accordingly, specific aims of this comprehensive proposal are: Aim 1: To develop an oligonucleotide-based approach to achieve efficient down-regulation of ET-1 in endothelial cells. ODN scanning arrays and ET-1 ELISA will be employed to identity - antisense ODNs that are highly efficient in inhibiting the ET-1 expression in mouse lung endothelial cells. In addition, RNA/DNA chimeric oligonucleotides will be investigated as an approach to achieve a long-term silencing of ET-1 in pulmonary endothelium. Aim 2: To develop novel delivery, systems to achieve efficient delivery of oligonucleotide to pulmonary endothelium with reduced toxicity. Aim 3: To investigate the biological effect of tissue-specific down-regulation of ET-1 in normal mice and in mice with PHT. The current proposal will lead to a better understanding of the roles of ET-1 in mouse hypoxia-induced pulmonary hypertension and provide experimental and preclinical support for rational pharmacogenetic approach to pulmonary hypertensive disorders. Down regulation of ET-1 biosynthesis by pulmonary endothelium by immunoliposome-mediated delivery of ODN may by itself, or in combination with" direct pulmonary vasorelaxants (e.g. nitric oxide and oxygen), provide an approach to prevent the progressive pathological aspects of PHT and ameliorate return towards more normal pulmonary vascular structure and function.